package org.apache.lucene.util;

import java.util.Comparator;
import java.util.StringTokenizer;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Methods for manipulating strings.
 *
 * @lucene.internal
 */
public abstract class StringHelper {
    /**
     * Expert:
     * The StringInterner implementation used by Lucene.
     * This shouldn't be changed to an incompatible implementation after other Lucene APIs have been used.
     */
    public static StringInterner interner = new SimpleStringInterner(1024, 8);

    /** Return the same string object for all equal strings */
    public static String intern(String s) {
        return interner.intern(s);
    }

    /**
     * Compares two byte[] arrays, element by element, and returns the
     * number of elements common to both arrays.
     *
     * @param bytes1 The first byte[] to compare
     * @param bytes2 The second byte[] to compare
     * @return The number of common elements.
     */
    public static final int bytesDifference(byte[] bytes1, int len1, byte[] bytes2, int len2) {
        int len = len1 < len2 ? len1 : len2;
        for (int i = 0; i < len; i++)
            if (bytes1[i] != bytes2[i])
                return i;
        return len;
    }

    private StringHelper() {
    }

    /**
     * @return a Comparator over versioned strings such as X.YY.Z
     * @lucene.internal
     */
    public static Comparator<String> getVersionComparator() {
        return versionComparator;
    }

    private static Comparator<String> versionComparator = new Comparator<String>() {
        public int compare(String a, String b) {
            StringTokenizer aTokens = new StringTokenizer(a, ".");
            StringTokenizer bTokens = new StringTokenizer(b, ".");

            while (aTokens.hasMoreTokens()) {
                int aToken = Integer.parseInt(aTokens.nextToken());
                if (bTokens.hasMoreTokens()) {
                    int bToken = Integer.parseInt(bTokens.nextToken());
                    if (aToken != bToken) {
                        return aToken < bToken ? -1 : 1;
                    }
                } else {
                    // a has some extra trailing tokens. if these are all zeroes, thats ok.
                    if (aToken != 0) {
                        return 1;
                    }
                }
            }

            // b has some extra trailing tokens. if these are all zeroes, thats ok.
            while (bTokens.hasMoreTokens()) {
                if (Integer.parseInt(bTokens.nextToken()) != 0)
                    return -1;
            }

            return 0;
        }
    };
}
